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Nomenclature for Cultivated Plants (ICNCP). Very few cannabis strains, however, have
met the ICNCP’s nomenclature requirements, and these rules will need to be applied to
cannabis strains in the future. While there may be a bit of a calm with respect to
cannabis taxonomy as implied by Small and McPartland (except for what might be
called excessive splitting after the subspecies level), it is doubtful that a “taxonomic
storm” can be avoided given the thousands of strains that might need to be systematized
by the codes of nomenclature. Stay tuned.
5
A Complicated Sex Life
How the cannabis plant develops from a fertilized ovule to a full-fledged reproducing
organism is a fascinating biological story. How populations of this plant form part of a
larger ecosystem and how cannabis, as a lineage, has changed through evolutionary time
are also big parts of its life history. The most logical place to start is the ovule (which
makes the egg) and the pollen grain (which produces the sperm), and then to work our
way up to the mature plant with its leaves, stems, and flowers. Eventually its seeds and
pollen start the cycle of development all over again.
Plant Porn
Flowering plants have diverse sex lives (fig. 5.1). To start, for flowering plants—that
is, plants that make flowers, like cannabis—all sex occurs within that flower. In fact,
the flower exists to facilitate effective reproduction with colors, scents, and nectar all
evolved to attract pollinators to the flower and effect pollination, or the placing of the
pollen in close proximity to the ovule so that sperm and egg can eventually meet to
result in fertilization. The pollen is produced in structures called stamens (see fig. 5.1,
male symbol), while the ovules are produced in structures called ovaries within the
pistil (see fig. 5.1, female symbol).
Figure 5.1. Drawings of typical monoecious and dioecious flowering plants. There are many ways a plant
can have its genitals structured. Very common among flowering plants are hermaphroditic flowers (left),
where both the stamen and pistils develop within the same flower. In this case, the flower has both male
(stamen) and female (pistil) reproductive structures. Other plants produce flowers that have either stamens
(male flowers) or pistils (female flowers), but not both. These are called imperfect or unisexual flowers. For
monoecious plants (middle), male and female flowers appear on the same plant. For dioecious plants
(right), a male plant produces only staminate flowers, while a separate female plant makes only pistillate
flowers. Adapted from Nefronus (Wikipedia drawing).
One aspect of the diversity of plant sex comes from that fact that some flowers
make both pollen and ovules, while others make only one or the other but not both. As
with humans and other animals, plants have two sexes that contribute to the reproduction
of the species. The two sexes make different gametes: the sperm (made by males) and
the egg (made by females). In plants, these two gametes can be produced by the same
individual as part of a single flower. The majority of the over 350,000 named flowering
plants are hermaphroditic, meaning the flowers produced have both stamen and pistils
(see fig. 5.1, left panel). However, some plants are what are called monoecious (“one
house”), where flowers are either staminate (male) or pistillate (female), and a single
individual produces both male and female flowers (see fig. 5.1, middle panel). This
state is more than likely the primitive state for flowering plants, meaning that the
common ancestor of all angiosperms was monoecious.
Cannabis uses this way of organizing its sex organs. But in a supersexed
evolutionary move, cannabis also features a different type of male/female sex system
called dioecious (“two houses”), whereby some plants make only female (pistillate)
flowers and others make only male (staminate) flowers (see fig. 5.1, right panel). About
7 percent of all flowering plants practice this kind of sex organization; compare this to
95 percent of all animals, which have a similar organization of the sexes called
gonochorism.
To dig a little deeper into the sex life of cannabis, I should point out its male plant
genitalia, the stamen (the pollen-bearing organ), is made of two major structures—the
anther and the filament. The anther carries the pollen, and the filament simply connects
the anther to the stem of the flower. The pistil of the female genitals is a bit more
complicated, with four major subparts: the stigma, style, ovary, and ovules.
I have oversimplified the flower sex morphology and breeding systems of plants,
because the names of the different breeding systems are daunting tongue twisters (see
table 5.1) and because for cannabis we only need to know that most individuals are
either strictly male or strictly female, although hermaphroditic flowers do arise
spontaneously in some marijuana breeding populations.
Overall, plants are much more “pansexual” than they are strictly dioecious or
monoecious. A fascinating aspect of these breeding systems is how they evolved.
Evolutionary botanist Susanne Renner points out that because pollen and stamens
appear in individuals for a large number of flowering plant lineages, bisexualism can be
considered the primitive state for flowering plants. She also suggests that there were
anywhere from 900 to 5,000 independent derivations of the different kinds of dioecy
that exist. This means that there was a lot of evolution from bisexuality to dioecious
breeding systems in plants.
If most cannabis plants today are dioecious, was the ancestor of all cannabis
dioecious? One way to decipher this is to examine the genus Cannabis’s closest relative
Humulus (hops). These plants are also mostly dioecious, with male and female flowers
strictly on different individuals. Bisexual flowers do occur at a very low frequency. The
most parsimonious interpretation, then, is that the breeding system of the hops/marijuana
common ancestor may have been a dioecious plant with separate sexes. Application of
different growth regulator chemicals to cannabis plants can alter the strict sexuality of
marijuana flowers, and this result implies that it is relatively easy to transition from a
population of plants with two sexes to a population that includes bisexual plants.
Physical and chemical stress can also induce the appearance of male-like flowers on
female cannabis plants. Stressors such as disrupted photoperiods and low temperature
may increase the formation of male flowers on female plants. That these environmental
and chemical stressors can spontaneously induce hermaphroditism offers another bit of
evidence for the primitive dioecious state of Cannabis and Humulus. The only factor
that is critical for the survival of a plant species such as cannabis is that there are some
male flowers and some female flowers in the population that will produce pollen and
ova. Seeds are produced by ova coming together with pollen. It shouldn’t matter
whether these flowers are on the same plant (monoecious) or on different plants
(dioecious). But this would be a naive assumption about the sex lives of plants, for
some plants can do “virgin birth” or parthenogenesis, when seeds are produced without
the act of fertilization. This brings us to a curious little debate from the 1800s as to
whether cannabis can reproduce parthenogenetically.
Table 5.1. THE SEVERAL KINDS OF PLANT SEX
Name Abundance Description
Monocliny 85 percent Perfect bisexual plants; flowers are truly bisexual
Distyly Rare Bisexual size of the male parts and female parts vary
Gynomonoecy Rare Female and hermaphroditic flowers on same individual
Gynodioecy Rare Female and hermaphroditic plants in same population
Monoecy < 7 percent Male flowers and female flowers on same plant
Dioecy < 6 percent Separate male and female individuals
Andromonoecy Rare Male and hermaphroditic flowers on the same plant
Androdioecy Rare Male and hermaphroditic plants in same population
Apparently Lazzarro Spallanzani of anti–spontaneous generation fame also worked
on cannabis, or what he called hemp. An Italian abbot, he was considered a careful
scientist and was responsible for debunking spontaneous generation (the hypothesis that
living organisms could develop from nonliving matter) in a series of experiments. He
tried similar experiments with plants, and it appeared as if cannabis could make seeds
without fertilization of the ovule by pollen-producing plants. In the 1800s French
botanist Charles Naudin repeated Spallanzani’s experiments with cannabis and found
the same results. Naudin also came within a hair’s breadth of discovering Mendel’s
principles of inheritance several decades before Mendel. If he had only thought of doing
crosses the way Mendel did, then the principles of segregation and random assortment
might be called Naudin’s laws instead of Mendel’s laws. In 1861 Hermann Karsten
repeated the observations of Naudin in a research paper and offered a much simpler
explanation for Naudin’s experimental results: “The researches of Naudin were
instituted on polygamous plants—a circumstance which naturally suggests to the mind
that a concealed male flower, or an anther produced in the interior of a female flower,
may have led the observer into error.”
Karsten was tough. In the 1861 paper he debunked several claims of virgin birth in
plants with relish. Here is his statement about researchers of his time who claimed
parthenogenesis occurred in plants: “Still, the propensity to credit what is marvellous,
and to excite an interest by taking up the defence of bold hypotheses at variance with
hitherto acknowledged laws, did not allow the results arrived at by the united assiduous
labours of so many naturalists to go unchallenged.” In other words, if you don’t have the
hard evidence, don’t bother us serious scientists with your unsupported hyperbole.
Although Karsten was a harsh critic of parthenogenesis in plants, he did
acknowledge its occurrence in algae and other lower plants. Today parthenogenesis has
been shown to occur in approximately 400 plant species, which would probably shock
Karsten. But he was right on one of these occasions: to date, virgin birth in cannabis has
not been validated despite the excitement over early experiments that suggested its
possibility. Today’s researchers are similarly excited about the possibility that genes
responsible for parthenogenesis might be useful targets for genetic engineering in
cannabis. Imagine a plant like cannabis that can reproduce parthenogenetically. That
would be a cannabis breeder’s dream—no male flowers needed and only buds (female
flowers) for generation after generation.
The pansexuality of cannabis is important in its commercial growth. Perhaps not so
much for those interested in growing hemp, but certainly for growers interested in the
recreational and medicinal aspects of marijuana. When a female plant’s ovules are
fertilized, its flowers set seed, which is an undesirable event for recreational and
medicinal cannabis. Growers will hunt for males (staminate flowers) in their crops and
remove them to prevent fertilization and subsequent seed production by the female
plants in the crop. Certainly, any hermaphroditic flowers are problematic too—
especially if some of the male genitalia are sneaky, such as those that fooled Spallanzani
and Naudin centuries ago.
Warehouses—Beyond Sex
So the sex life of cannabis is complex. But to say that the development of the cannabis
plant itself is complex is an understatement. To simplify or codify its development,
agronomist Vito Mediavilla and colleagues devised a digital system for designating the
developmental stages of the cannabis plant (table 5.2). Basically, there are four major
developmental stages:
Stage 0000 Germination and emergence
Stage 1000 Vegetative stage
Stage 2000 Flowering and seed formation
Stage 3000 Senescence
Each of the base stages (0, 1, 2, and 3) can be subdivided into further substages by the
addition of numbers in the second, third, and fourth positions. So 1100 refers to stage 1,
substage 1.
Most cannabis researchers and enthusiasts recognize these stages in some way, but
what Mediavilla and colleagues managed to do was categorize the developmental
stages using a digital coding system, enabling a more precise description of cannabis
development. In this chapter we will look closely at stage 0 and stage 1, where
cannabis’s developmental program is kick-started.
The unfertilized ovule and the pollen grains are strange kinds of cells compared
with the rest of the cells in the adult cannabis plant. Adult plant cells not involved in
reproduction have two copies of every gene in their genome and are called diploid. The
cells involved in reproduction—pollen and ovules—have a single copy of their genes
and are called haploid. A seed, otherwise known as a fertilized ovule, is the product of
a single pollen tube penetrating the ovule’s outer membrane and releasing a sperm cell
that fuses with the ovule’s egg. The pollen’s haploid genome (via the sperm) is released
into the interior of the ovule, where the ovule’s haploid genome (via the egg) fuses with
the sperm to form the nucleus of a single fertilized diploid cell. This diploid cell is
called a zygote, which will develop to become the embryo and eventually the seedling.
In this sense, the overall nuclear genome of a diploid organism is formed by biparental
inheritance (one-half of the new genome from the pollen/sperm and one-half of the
genome from the ovule/egg). Here again, plants are notorious for violating this mode of
diploid union by increasing the number of chromosomes or genomes that reside in their
parents. These kinds of increases cause what is called polyploidy.
Table 5.2. MEDIAVILLA AND COLLEAGUES’ DIGITALIZED DEVELOPMENT SCHEME FOR CANNABIS
Code Description Remarks
Stage0Germination and
emergence
0000 Dry seed
0001 Radicle apparent
0002 Emergence of
hypocotyl
0003 Cotyledons unfolded
Stage1Vegetative stage Refers to main stem; leaves are considered as unfolded when leaflets
are at least 1 cm long
1002 1st leaf pair 1 leaflet
1004 2nd leaf pair 3 leaflets
1006 3rd leaf pair 5 leaflets
1008 4th leaf pair 7 leaflets
1010 5th leaf pair
Stage2Flowering and seed
formation
Refers to the main stem, including branches
Code Description Remarks
2000 GV point Change of phyllotaxis on the main stem from opposite to alternate
2001 Flower primordia Sex nearly indistinguishable
Dioecious plant—male
2100 Flower formation First closed staminate flowers
2101 Beginning of flowering First opened staminate flowers
2102 Flowering 50% opened staminate flowers
2103 End of flowering 95% of staminate flowers open or withered
Dioecious plant—female
2200 Flower formation First pistillate flowers; bract with no styles
2201 Beginning of flowering Styles of first female flowers
2202 Flowering 50% of bracts formed
2203 Beginning of seed
maturity
First seeds hard
2204 Seed maturity 50% of seeds hard
2205 End of seed maturity 95% of seeds hard or shattered
Monoecious plant
2300 Female flower
formation
2301 Beginning of female
flowering
First pistillate flowers; perigonal bract with no pistils
2302 Female flowering 50% of bracts formed
2303 Male flower formation First closed staminate flowers
2304 Male flowering Most staminate flowers open
2305 Beginning of seed
maturity
First seeds hard
2306 Seed maturity 50% of seeds hard
2307 End of seed maturity 95% of seeds hard or shattered
Stage3Senescence
3001 Leaf desiccation Leaves dry
3002 Stem desiccation Leaves dropped
3003 Stem decomposition Bast fibers free
Cannabis generally avoids polyploidy, and in the wild it is found only as a diploid.
Most cultivars to date are also diploid. But there are advantages to polyploidization. In
domestic plants such as wheat and barley, random ancient polyploidization events have
been essential to the age-old cultivation and popularity of these plants. In modern plant
breeding the process of polyploidization can overcome species boundaries and allow
interspecific hybrids to form—that is, new plant species can be formed by the
successful reproduction of two separate species that maintain the genomes of both
parental plants. Such polyploid hybrids are often important in plant breeding because
they produce novel plant phenotypes that neither parent is able to produce.
Polyploidization is also important in generating seedless cultivars (such as bananas or
grapes) and can increase the resistance or tolerance of a plant to drought or poor soils.
It is no surprise that agronomic research on the effects of polyploidy in cannabis has
recently begun. Using various chemicals known to generate polyploid cells, Jessica
Parsons and colleagues have found ways to produce tetraploid (four genomes) cannabis.
Their research shows that leaves of tetraploid plants are larger than those of diploids
and yet only half as dense. Most important, CBD content increases by an average of 9
percent in the tetraploid plants, but there is no observed increase or decrease in THC
content. Tetraploid cannabis also has significant alterations of terpene profiles, which
are important characteristics of both recreational and medicinal cannabis. As such,
polyploid cannabis could produce a rich source of variation for cultivated marijuana.
Both pollen and ovules have two small organelles called mitochondria and
chloroplasts in their cytoplasm, as discussed in chapter 3. Chloroplasts are involved in
photosynthesis, which produces food in the form of sugars for the plant, and
mitochondria are involved in respiration, a key component of energy production.
Chloroplasts and mitochondria contain small circular pieces of DNA that are referred
to, respectively, as the plastid (chloroplast) and mitochondrial genomes. Pollen grains
do not tend to have chloroplasts because they do not undergo photosynthesis and are
quite small and short-lived. As a result, the sperm itself has a nuclear genome from the
parent plant but often does not bring with it a mitochondrial or a plastid genome. On the
contrary, the egg has both a mitochondrial and a plastid genome, since both organelles
are present in the ovule. The mitochondria and chloroplasts are inherited in effectively
uniparental or clonal manners—with only maternal inheritance of their organellar
genomes.
In order for a single fertilized egg to develop to a full-fledged cannabis plant with
billions of cells, it obviously needs to produce more cells. The unfertilized ovule, with
its egg nucleus inside, acts as a warehouse for DNA, encoding the proteins responsible
for growth but also for many proteins that the ovule has manufactured to ensure that the
seedling survives. Unfertilized ovules cannot make more cells, because they don’t have
the right molecular signals until they are fertilized. The signals to start cellular division
occur when the two haploid genomes of the sperm and egg interact with each other to
form the diploid genome of the developing zygote. Once the signals are right, the
fertilized ovule starts to divide and to produce new patches of cells and structures (fig.
5.2). This will eventually become the seed, with the embryo inside.
Figure 5.2. Drawing of a typical cannabis seed (left) with interior parts labeled on a longitudinal section in the
center and a transverse section labeled on the right. Redrawn from Helga Mölleken and Roland R. Theimer,
“Survey of Minor Fatty Acids in Cannabis sativa L. Fruits of Various Origins,” Journal of the International
Hemp Association 4, no. 1 (1997): 13–18.
Once fertilization has occurred, a seed is formed, inside of which the embryo
develops. It develops to a point and then stops and waits for germination. Germination
is when the embryo inside the seed will burst out from the seed coat and establish itself
as a seedling.
The seed is composed of a seed coat or pericarp, along with the developing
embryo inside. The embryo includes rudimentary leaves called cotyledons (fig. 5.3);
these first leaves do different things in different species, but always with the goal of
nourishing the developing seedling. In some, they emerge from the germinating seed to
be the first leaves to undergo photosynthesis. In others, they stay inside the pericarp and
become filled with embryo-nourishing starches (as with walnuts and peanuts). In both
cases, a rich complement of proteins made by the mother plant resides in the seed.
Estimates of the number of different kinds of proteins in the unfertilized ovule of
cannabis range from about 168 to 181, depending on the cultivar and on the
environments where the plants are found. Much of the research so far has been done on
hemp cultivars (that is, strains with less than 0.3 percent THC concentration) because of